×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Earth Fault Relay Problem

Earth Fault Relay Problem

Earth Fault Relay Problem

(OP)
Hi all,
We have some CDG26 Earth Fault relays ( tap range 0.1 to 0.4A, DMT 3 sec) on our system and one of them has failed to trip on a feeder, as a result an upstream transformer has tripped.
We investigated the relay and found out that the relay performs quite satisfactory if tested with conventional injection units.
It is a high burden relay and was tested up to 10 times tap setting with correct operation.
The fault level that had been experienced was more than 10 times, probably around 20 times the tap setting. At that point the relay had maloperation.
We tried to simulate the situation by testing relay @ 20 times tap setting and using a variac and two back to back CTs (ratios: 10/500 and 500/2) in the circuit instead of an electronic test unit. This time the voltage developed across the relay coil was around 100Volts and the disc did not move at all.
Now can I conclude that in the real fault situation, the fault has generated a large voltage across the coil and had shorted the tap contacts and prevented the relay from operation?
If the fault level goes above 10 times tap setting, these relays will not be reliable for the application, as their accuracy of tripping is only up to 10 times. Should we consider phasing them out and replacing them with low burden earth fault relays?
Any ideas? Thanks

RE: Earth Fault Relay Problem

1.What is your fault level?
2.What is your CT's ratios, burdens and accuracies?

The 10% tap (0.1A) on the 10%-40% CDG26 relay (normal inverse relay) have at 10 times current a impedance of approx:
       
           100 Ohms for 3VA relay (50Hz)
            30 Ohms for 1VA relay (50Hz)

Your CT's must be able to supply a secondary voltage required to drive the current through this high impedance - to operate the relay. Make sure your CT's don't saturate under fault conditions.

The older type of relays (electromechanical) have a high burden. (lower tap setting = higher burden)  The new type of relays (electronic relays) have a very low burden.

Maybe it is beter to have new relays, but throughout all the years the older relays were very reliable, so make sure you are not replacing them unnecessary.


RCC

RE: Earth Fault Relay Problem

I agree with RalphChristie: don't replace just because the relays are older EM-type.

I would want to know a bit more about the system you are controling: LV, MV, HV?  What is the industry?  Is the application utility, industrial or commercial?

If you do upgrade relays, this will determine what level the relays need to be (GE vs. Bender; Basler vs. Cutler-Hammer; etc.)

RE: Earth Fault Relay Problem

(OP)
Huntercon,
The system is a 132KV utility. I am trying to get the fault levels at that point. Haven't got them yet.
If the relays are to be changed, they will be replaced with Alstom relays MCGG.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

White Paper - Smart Manufacturing for Semiconductor
New technologies and approaches present great opportunities for semiconductor manufacturers to achieve high levels of innovation, yield and improvement. This white paper explores some of these cutting-edge technologies and how they can be applied effectively in the semiconductor industry. Read about how Smart Manufacturing is transforming the semiconductor industry. Download Now
White Paper - Analysis and Simulation in Aircraft Structure Certification
Organizations using simulation and analysis tools effectively see the benefits in their ability to achieve certification faster and with drastically less total cost than those who do not maximize these tools. Read this White Paper to learn about how digital tools such as analysis and simulation help in aircraft structure certification. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close